Q: Why Do We Wear Pants? A: Horses

Whence came pants? I'm wearing pants right now. There's a better than 50 percent chance that you, too, are wearing pants. And neither of us have probably asked ourselves a simple question: Why?

It turns out the answer is inexplicably bound up with the Roman Empire, the unification of China, gender studies, and the rather uncomfortable positioning of man atop horse, at least according to University of Connecticut evolutionary biologist Peter Turchin.

"Historically there is a very strong correlation between horse-riding
and pants," Turchin wrote in a blog post this week. "In Japan, for example, the traditional dress is kimono, but
the warrior class (samurai) wore baggy pants (sometimes characterized as
a divided skirt), hakama. Before the introduction of horses by
Europeans (actually, re-introduction - horses were native to North
America, but were hunted to extinction when humans first arrived there),
civilized Amerindians wore kilts."

The reasons why pants are advantageous when mounted atop a horse should be obvious, nonetheless, many cultures struggled to adapt, even when their very existences were threatened by superior, trouser-clad horseback riders.

Turchin details how the Romans eventually adopted braccae (known to you now as breeches) and documents the troubles a 3rd-century BC Chinese statesman, King Wuling, had getting his warriors to switch to pants from the traditional robes. "It is not that I have any doubt concerning the dress of the Hu," Wuling told an advisor. "I am afraid that everybody will laugh at me." Eventually, a different state, the Qin, conquered and unified China. They just so happened to be closest to the mounted barbarians and thus were early to the whole cavalry-and-pants thing.

Turchin speculates that because mounted warriors were generally men of relatively high status, the culture of pants could spread easily throughout male society.

I'd add one more example from history: the rise of the rational dress movement in conjunction with the widespread availability of the bicycle. Here's a University of Virginia gloss:

The advent and the ensuing popularity of the safety bicycle, with its
appeal to both sexes mandated that women cast off their corsets and
figure out some way around their long, billowy skirts. The answer to the
skirt question was to be found in the form of bloomers, which were
little more than very baggy trousers, cinched at the knee. Bloomers
provoked wrath in conservatives and delight in women cyclists, and the
garment was to become the centerpiece of the "rational dress" movement
that sprung up at the end of the 19th century.

What all these examples suggest is that technological systems -- cavalry, bicycling -- sometimes require massive alterations in a society's culture before they can truly become functional. And once it's locked in, the cultural solution (pants) to an era's big problem can be more durable than the activity (horse-mounted combat) that prompted it.